U.S. patent application number 10/860902 was filed with the patent office on 2005-08-18 for method and system for performing more consistent switching of magnetic elements in a magnetic memory.
Invention is credited to Le, Son, Min, Tai, Shi, Xizeng, Wang, Po-Kang.
Application Number | 20050180201 10/860902 |
Document ID | / |
Family ID | 34841158 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050180201 |
Kind Code |
A1 |
Shi, Xizeng ; et
al. |
August 18, 2005 |
Method and system for performing more consistent switching of
magnetic elements in a magnetic memory
Abstract
A method and system for programming a magnetic memory is
disclosed. The method and system further include turning on a word
line current and turning on a bit line current. The word line
current is for generating at least one hard axis field. The bit
line current is for generating at least one easy axis field. In one
aspect, the method and system further include turning off the word
line current and the bit line current such that a state of the at
least one magnetic memory cell is repeatably obtained. In another
aspect, the word line current is turned off after the bit line
current is turned off.
Inventors: |
Shi, Xizeng; (Fremont,
CA) ; Le, Son; (Gilroy, CA) ; Wang,
Po-Kang; (San Jose, CA) ; Min, Tai; (San Jose,
CA) |
Correspondence
Address: |
SAWYER LAW GROUP LLP
P.O. Box 51418
Palo Alto
CA
94303
US
|
Family ID: |
34841158 |
Appl. No.: |
10/860902 |
Filed: |
June 3, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60544152 |
Feb 13, 2004 |
|
|
|
Current U.S.
Class: |
365/158 |
Current CPC
Class: |
G11C 11/16 20130101 |
Class at
Publication: |
365/158 |
International
Class: |
G11C 011/00 |
Claims
What is claimed is:
1. A method for programming at least one magnetic memory cell
comprising: (a) turning on a word line current for generating at
least one hard axis field; (b) turning on a bit line current, the
bit line current for generating at least one easy axis field; and
(c) turning off the word line current and the bit line current such
that a state of the at least one magnetic memory cell is repeatably
obtained.
2. The method of claim 1 wherein step (b) further includes the step
of: (b1) turning the bit line current on after the word line
current is turned on.
3. The method of claim 2 wherein the turning off step (c) further
includes the step of: (c1) turning off the word line current and
the bit line current such that the word line current reaches zero
after the bit line current reaches zero.
4. The method of claim 2 wherein turning on step (a) further
includes the step of: (a1) turning the word line current on to a
first value; and wherein the turning off step (c) further includes
the steps of (c1) turning the word line current to a second value
less than the first value and greater than zero after the bit line
current is turned on in step (b); (c2) turning the bit line current
off while the word line current is at the second value; and (c3)
turning the word line current off after the bit line current is
turned off in step (c2).
5. The method of claim 2 wherein turning off step (c) further
includes the step of: (c1) gradually decreasing the word line such
that the word line current reaches zero after the bit line current
is zero.
6. The method of claim 2 wherein the turning off step (c) further
includes the step of: (c1) turning the bit line current off; and
(c2) turning the word line current off after the bit line current
has been turned off.
7. A magnetic memory comprising: a plurality of magnetic memory
cells; and at least one current source for providing a word line
current and a bit line current for programming at least one
magnetic memory cell of the plurality of magnetic memory cells, the
word line current for generating at least one hard axis field, the
bit line current for generating at least one easy axis field, the
at least one current source for turning on the word line current,
for turning on a bit line current after the word line current is
turned on, and for turning off the word line current and the bit
line current such that a state of the at least one magnetic memory
cell is repeatably obtained.
8. The magnetic memory of claim 7 wherein the at least one current
source further turns the bit line current on after the word line
current is turned on.
9. The magnetic memory of claim 8 wherein the at least one current
source further turns off the word line current and the bit line
current such that the word line current reaches zero after the bit
line current reaches zero.
10. The magnetic memory of claim 8 wherein the at least one current
source further turns the word line current and the bit line current
off such that the at least one current source turns the word line
current on to a first value, turns the word line current to a
second value less than the first value and greater than zero after
the bit line current is turned on, turns the bit line current off
while the word line current is at the second value, and turns the
word line current off after the bit line current is turned off.
11. The magnetic memory of claim 8 wherein the at least one current
source further turns the word line current and the bit line current
off such that the at least one current source gradually decreases
the word line such that the word line current reaches zero after
the bit line current is zero.
12. The magnetic memory of claim 8 wherein the at least one current
source further turns the word line current and the bit line current
off such that the at least one current source turns the bit line
current off and then turns the word line current off after the bit
line current has been turned off.
13. A method for programming at least one magnetic memory cell
comprising: (a) turning on a word line current for generating at
least one hard axis field; (b) turning on a bit line current, the
bit line current for generating at least one easy axis field; and
(c) turning off the bit line current; (c) turning off the word line
current after the bit line current is turned off.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is claiming under 35 USC 119(e) the benefit
of provisional patent application Ser. No. 60/544,152 filed on Feb.
13, 2004.
FIELD OF THE INVENTION
[0002] The present invention pertains to reading nonvolatile
magnetic memories, such as a magnetic random access memory (MRAM),
and more particularly to a method and system for providing a more
reliable switching of magnetic elements in the magnetic
memories.
BACKGROUND OF THE INVENTION
[0003] FIG. 1 depicts a conventional magnetic element 10 used in
conventional magnetic memories, such as magnetic random access
memories (MRAM). The conventional magnetic element 10 includes a
conventional pinned layer 12, a conventional tunneling barrier 14,
and a conventional free layer 16. Other layers (not shown), such as
antiferromagnetic pinning, seed, and/or capping layers may also be
used. The conventional pinned layer 12 and the conventional free
layer 18 are ferromagnetic. Thus, the conventional free layer 16 is
depicted as having a changeable magnetization 17. The conventional
spacer layer 14 is a nonmagnetic tunneling barrier layer. The
magnetization 13 of the pinned layer 12 is pinned in a particular
direction. The magnetization 17 of the free layer 16 is free to
rotate, typically in response to an external magnetic field.
[0004] The geometry of the conventional magnetic element 10 is such
that the magnetization 17 of the conventional free layer 16 is
stable parallel or antiparallel to the magnetization 13 of the
conventional pinned layer 12. Depending upon the orientations of
the magnetization 17 of the conventional free layer 16 and the
magnetization 13 of the conventional pinned layer 12, the
resistance of the conventional magnetic element 10 changes. When
the magnetization 17 of the conventional free layer 16 is parallel
to the magnetization 13 of the conventional pinned layer 12, the
resistance of the conventional magnetic element 10 is low and, in
general, the magnetic element 10 is in a "0" state. When the
magnetization 17 of the conventional free layer 16 is antiparallel
to the magnetization 13 of the conventional pinned layer 12, the
resistance of the conventional magnetic element 10 is high and the
conventional magnetic element 10 is in a "1" state.
[0005] In order to write to the conventional magnetic element 10,
two currents, or equivalently, two fields are typically used. One
field is typically perpendicular to the final, equilibrium
direction of the magnetization 17 of the conventional free layer
16. This field is known as the hard axis field and is typically
generated by a word line current driven in a corresponding word
line. The other field is typically parallel or antiparallel to the
magnetization 13 of the conventional pinned layer 12. This field is
known as the easy axis field and is typically generated by a bit
line current driven in a corresponding bit line. Depending on the
direction of the bit line current (e.g. positive or negative with
respect to a particular defined current direction), the
magnetization 17 of the conventional free layer 16 is aligned
generally parallel or generally antiparallel to the magnetization
13 of the conventional pinned layer 12.
[0006] FIG. 1B depicts a conventional method 50 for programming the
conventional magnetic element 10. FIG. 1C depicts a graph
indicating the word line current and bit line current corresponding
to the conventional method 50. At some time, the word line current
I1 is turned on, via step 52. Consequently, a hard axis field
corresponding to I1 is generated. After some later time, t1, the
bit line current I2 (or '1I2) is turned on, via step 54. Thus, an
easy axis field in the appropriate direction is generated. Both
currents remain on for some time, t2. The word line current is then
turned off, via step 56. After some time, t3, after the word line
current has been completely turned off, the bit line current is
turned off, via step 58.
[0007] Although the conventional method 50 allows the conventional
magnetic element 10 to be programmed, one of ordinary skill in the
art will readily realize that there are drawbacks to such
programming. FIGS. 2A-2C depict the free layer 60, 60' and 60" of
the conventional magnetic element 10 after the conventional method
50 has been used. The same currents were used in steps 52 and 54
for the free layer 60, 60' and 60". As can be seen in FIGS. 2A-2C,
the majority of the magnetic moments for each of the free layers
60, 60' and 60" are aligned in the same direction. However, due to
the demagnetization field at the ends of the free layers 60, 60',
and 60", the magnetization near the left and right ends of the free
layers 60, 60', and 60", respectively, are not perpendicular to the
surfaces at the ends of the free layers 60, 60', and 60",
respectively. Instead, the magnetic moments 62 and 64, 62' and 64',
and 62" and 64" may have different orientations. The free layer 60
has the magnetic moments 62 and 64 parallel. The magnetic moments
62' and 64' of the free layer 60' are not parallel. Although the
magnetic moment 62' is in the same direction as the magnetic moment
62, the magnetic moment 64' is in a different direction. Similarly,
the magnetic moments 62" and 64" of the free layer 60' `are not
parallel. Although the magnetic moment 64' is in the same direction
as the magnetic moment 64, the magnetic moment 62" is in a
different direction.
[0008] The differences in the magnetic moments 62 and 64, 62' and
64', and 62" and 64" cause the free layers 60, 60', and 60",
respectively, to be switched at different fields and, therefore,
programming failures. Stated differently, even when programmed in
the same way using the conventional method 50, the magnetic moments
62 and 64, 62' and 64', and 62" and 64" may differ. Consequently,
the fields required to switch the magnetizations may differ. As a
result, the bit line currents and word line currents required to
program the free layers 60, 60', and 60" differ. When the switching
field increases, the currents actually used may not be sufficient
to program the free layer 60, 60', or 60". Conversely, when the
switching field decreases, the currents actually used may cause
inadvertent programming of the free layer 60, 60', or 60".
[0009] Accordingly, what is needed is a system and method for more
reliably programming elements in a magnetic memory. The present
invention addresses such a need.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method and system for
programming a magnetic memory. The method and system further
include turning on a word line current and turning on a bit line
current. The word line current is for generating at least one hard
axis field. The bit line current is for generating at least one
easy axis field. In one aspect, the method and system further
include turning off the word line current and the bit line current
such that a state of the at least one magnetic memory cell is
repeatably obtained. In another aspect, the word line current is
turned off after the bit line current is turned off. According to
the system and method disclosed herein, the present invention
provides a method that allows repeatable programming of magnetic
memories such that inadvertent programming and programming failures
are reduced or eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is a diagram of a conventional magnetic element used
in a magnetic memory.
[0012] FIG. 1B is a flow chart depicting a conventional method for
programming a conventional magnetic storage cell in a conventional
magnetic memory.
[0013] FIG. 1C is a graph depicting the hard axis and easy axis
currents versus time for programming of a conventional magnetic
storage cell in a conventional magnetic memory.
[0014] FIG. 2A depicts one possible magnetization distribution for
the conventional free layer of one conventional magnetic element
programmed using a conventional method.
[0015] FIG. 2B depicts another possible magnetization distribution
for the conventional free layer of one conventional magnetic
element programmed using a conventional method.
[0016] FIG. 2C depicts a third possible magnetization distribution
for the conventional free layer of one conventional magnetic
element programmed using a conventional method.
[0017] FIG. 3 is a high-level flow chart depicting one embodiment
of a method in accordance with the present invention for more
consistently programming a magnetic storage cell in a magnetic
memory.
[0018] FIG. 4A is a more detailed flow chart depicting a first
embodiment of a method in accordance with the present invention for
more consistently programming a magnetic storage cell in a magnetic
memory.
[0019] FIG. 4B is a graph depicting the word line and bit line
currents versus time for programming of a magnetic storage cell in
a magnetic memory using the first embodiment of the method in
accordance with the present invention.
[0020] FIG. 4C is another graph depicting the word line and bit
line currents versus time for programming of a magnetic storage
cell in a magnetic memory using the first embodiment of the method
in accordance with the present invention.
[0021] FIG. 5A is a more detailed flow chart depicting a second
embodiment of a method in accordance with the present invention for
more consistently programming a magnetic storage cell in a magnetic
memory.
[0022] FIG. 5B is a graph depicting the word line and bit line
currents versus time for programming of a magnetic storage cell in
a magnetic memory using the second embodiment of the method in
accordance with the present invention.
[0023] FIG. 6A is a more detailed flow chart depicting a third
embodiment of a method in accordance with the present invention for
more consistently programming a magnetic storage cell in a magnetic
memory.
[0024] FIG. 6B is a graph depicting the word line and bit line
currents versus time for programming of a magnetic storage cell in
a magnetic memory using the third embodiment of the method in
accordance with the present invention.
[0025] FIG. 7A is a graph depicting a write-read test using one
embodiment of the method in accordance with the present invention
for programming a magnetic memory.
[0026] FIG. 7B is a graph depicting a write-read test using a
conventional method for programming a magnetic memory.
[0027] FIG. 8 is a high-level block diagram of one embodiment of a
system in accordance with the present invention for programming a
magnetic storage cell in a magnetic memory.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The present invention relates to an improvement in
programming of magnetic memories. The following description is
presented to enable one of ordinary skill in the art to make and
use the invention and is provided in the context of a patent
application and its requirements. Various modifications to the
preferred embodiment will be readily apparent to those skilled in
the art and the generic principles herein may be applied to other
embodiments. Thus, the present invention is not intended to be
limited to the embodiment shown, but is to be accorded the widest
scope consistent with the principles and features described
herein.
[0029] The present invention provides a method and system for
programming a magnetic memory. The method and system further
include turning on a word line current and turning on a bit line
current. The word line current is for generating at least one hard
axis field. The bit line current is for generating at least one
easy axis field. The method and system further include turning off
the word line current and the bit line current such that a state of
the at least one magnetic memory cell is repeatably obtained.
[0030] The present invention will be described in terms of a
particular magnetic element. However, one of ordinary skill in the
art will readily recognize that this method and system will operate
effectively for other magnetic elements, including but not limited
to spin valves. The present invention is also described in the
context of particular methods having certain steps. However, one of
ordinary skill in the art will readily recognize that the method
may include other and/or additional steps not inconsistent with the
present invention. Moreover, the present invention is described in
terms of word lines and bit lines. However, one of ordinary skill
in the art will readily recognize that these names may be
interchanged.
[0031] To more particularly illustrate the method and system in
accordance with the present invention, refer now to FIG. 3,
depicting a high-level flow chart of one embodiment of a method 100
in accordance with the present invention for more consistently
programming a magnetic storage cell in a magnetic memory. The
method 100 is described in the context of programming a single
memory cell. However, one of ordinary skill in the art will readily
recognize that the method can be used for multiple memory cells,
for example by utilizing a multiple bit line currents. A word line
current is turned on, via step 102. The word line current generates
the hard axis field used in programming a memory cell. The
appropriate bit line current is turned on, via step 104. Preferably
step 104 turns the bit line current on after the word line current
has been turned on. The bit line current generates the easy axis
field. Thus, the sign of the bit line current (positive or
negative) sets the direction of the easy axis field and, therefore,
the state of the magnetic memory cell. The word line current and
the bit line current are turned off such that a state of the at
least one magnetic memory cell is repeatably obtained, via step
106. As defined herein a state of a magnetic memory cell is
repeatably obtained when the magnetic moments, including magnetic
moments at the ends of the magnetic memory cell, are in
substantially the same direction when a particular state (e.g. a
"0" or "1") is programmed to the magnetic memory cell. Step 106
preferably occurs after a desired time interval has passed since
the bit line current was turned on. In addition, step 106
preferably turns the word line current and the bit line current off
such that the word line current reaches zero after the bit line
current reaches zero.
[0032] The method 100 allows for more repeatable programming of
magnetic memory cells. Because step 106 turns the word line current
and bit line current off such that a state of the magnetic memory
cell is repeatably obtained (or turns the word line current off
after the bit line current has been turned off), inadvertent
writing and programming failures may be reduced or eliminated. In
particular, the magnetic moments within the magnetic memory cell,
including those at the edges of the magnetic memory cell, are
substantially the same for a particular state of the magnetic
memory cell. In a preferred embodiment, the word line current and,
therefore, the hard axis field are turned off after the bit line
current and easy axis field. As a result, the magnetic moments at
the edges of the memory cell will be substantially the same for a
particular state of the magnetic memory cell. For example, the free
layer 60 depicted in FIG. 2A may be repeatably obtained. In other
words, the moments 62 and 64 will be in substantially the direction
shown in FIG. 2A. The configurations depicted in FIGS. 2B and 2C
may generally be avoided. Thus, the field at which the magnetic
memory cell will switch is substantially the same. Consequently,
the hard and easy axis fields, and the corresponding currents,
required to program the memory cell will be substantially the same.
The state and, therefore, programming of the magnetic memory cell
can thus be repeatably obtained.
[0033] FIG. 4A is a more detailed flow chart depicting a first
embodiment of a method 110 in accordance with the present invention
for more consistently programming a magnetic storage cell in a
magnetic memory. The method 110 is described in the context of
programming a single memory cell. However, one of ordinary skill in
the art will readily recognize that the method can be used for
multiple memory cells, for example by utilizing a multiple bit line
currents. A word line current is turned on to a first value, via
step 112. The word line current generates the hard axis field used
in programming a memory cell. The appropriate bit line current is
turned on, via step 114. Preferably step 114 turns the bit line
current on after the word line current has been turned on. The bit
line current generates the easy axis field. Thus, the sign of the
bit line current (positive or negative) sets the direction of the
easy axis field and, therefore, the state of the magnetic memory
cell. The word line current is reduced to a second value that is
less than the first value, via step 116. Step 116 preferably occurs
after a desired time interval has passed since the bit line current
was turned on. The bit line current is turned off, via step 118.
After the bit line current has been turned off, the word line
current is turned, via step 120.
[0034] FIG. 4B is a graph 122 depicting the word line current 124
and bit line current 126 versus time for programming of a magnetic
storage cell in a magnetic memory using the first embodiment of the
method 110 in accordance with the present invention. FIG. 4C is a
graph 122' depicting the word line current 124' and bit line
current 126' versus time for programming of a magnetic storage cell
in a magnetic memory using the first embodiment of the method in
accordance with the present invention. Referring to FIGS. 4B and
4C, note that the bit line current 126' is negative, while the bit
line current 126 is positive. Thus, the bit line currents 126 and
126' are simply used to program the memory cell, such as one
including the conventional magnetic element 10, to different
states. Also in a preferred embodiment, Iw1 equals Iw1', Ib1 equals
Ib1', t1 equals=t1', t2 equals t2', t3 equals t3', t4 equals t4',
and t5 equals t5'. As can be seen in FIGS. 4B and 4C, the word line
current 124/124' is turned on to a value Iw1/Iw1', respectively, at
a time t1/t1', respectively. An amount of time later, t2/t2', the
bit line current 126/126', respectively, is turned on to Ib1/Ib1'.
At an amount of time, t3/t3', later the word line current 124/124',
respectively, is reduced to a lower value, Iw2/Iw2', respectively.
The bit line current 126/126' is turned off at an amount of time
t4/t4', respectively, later. Finally, the word line current
124/124' is turned off an amount of time, t5/t5' later.
[0035] Because the word line current 124/124' is turned off after
the bit line current 126/126' in step 120, the method 110 allows
for more repeatable programming of magnetic memory cells. The word
line current and, therefore, the hard axis field are turned off
after the bit line current and easy axis field. As a result, the
magnetic moments at the edges of the memory cell will be
substantially the same for a particular state of the magnetic
memory cell. For example, the free layer 60 depicted in FIG. 2A may
be repeatably obtained. In other words, the moments 62 and 64 will
be in substantially the direction shown in FIG. 2A. The remaining
configurations depicted in FIGS. 2B and 2C may generally be
avoided. Thus, the field at which the magnetic memory cell will
switch is substantially the same. Consequently, the hard and easy
axis fields, and the corresponding currents, required to program
the memory cell will be substantially the same. The state and,
therefore, programming of the magnetic memory cell can thus be
repeatably obtained.
[0036] FIG. 5A is a more detailed flow chart depicting a second
embodiment 130 of a method in accordance with the present invention
for more consistently programming a magnetic storage cell in a
magnetic memory. The method 130 is described in the context of
programming a single memory cell. However, one of ordinary skill in
the art will readily recognize that the method can be used for
multiple memory cells, for example by utilizing a multiple bit line
currents. A word line current is turned on, via step 132. The word
line current generates the hard axis field used in programming a
memory cell. The appropriate bit line current is turned on, via
step 134. Preferably step 134 turns the bit line current on after
the word line current has been turned on. The bit line current
generates the easy axis field. Thus, the sign of the bit line
current (positive or negative) sets the direction of the easy axis
field and, therefore, the state of the magnetic memory cell. The
word line current is gradually reduced and the bit line current
turned off such that the word line current is turned off (reaches
zero) after the bit line current reaches zero, via step 136. Step
136 preferably commences occurs after a desired time interval has
passed since the bit line current was turned on. Also in a
preferred embodiment, the word line current is decreased in a
linear fashion.
[0037] FIG. 5B is a graph 140 depicting the word line current 142
and bit line current 144 versus time for programming of a magnetic
storage cell in a magnetic memory using the second embodiment of
the method 130 in accordance with the present invention. The word
line current 142 is turned on to a value of Iw3 at time t1". At
time t2" later, the bit line current 144 is turned on to a value of
Ib2. At a time, t3", later the gradual reduction of the word line
current 142 is commenced to reduce the word line current 142 from
Iw3 to zero. In the graph 140 depicted, the word line current is
reduced in a linear fashion. The bit line current 144 is turned off
at time t4" later, before the word line current 142 has reached
zero. At a time, t5", later the word line current 142 reaches
zero.
[0038] Because the word line current 142 is turned off after the
bit line current 144 in step 136, the method 130 allows for more
repeatable programming of magnetic memory cells. The word line
current and, therefore, the hard axis field are turned off after
the bit line current and easy axis field. As a result, the magnetic
moments at the edges of the memory cell will be substantially the
same for a particular state of the magnetic memory cell. For
example, the free layer 60 depicted in FIG. 2A may be repeatably
obtained. In other words, the moments 62 and 64 will be in
substantially the direction shown in FIG. 2A. The remaining
configurations depicted in FIGS. 2B and 2C may generally be
avoided. Thus, the field at which the magnetic memory cell will
switch is substantially the same. Consequently, the hard and easy
axis fields, and the corresponding currents, required to program
the memory cell will be substantially the same. The state and,
therefore, programming of the magnetic memory cell can thus be
repeatably obtained.
[0039] FIG. 6A is a more detailed flow chart depicting a third
embodiment of a method in accordance with the present invention for
more consistently programming a magnetic storage cell in a magnetic
memory. The method 150 is described in the context of programming a
single memory cell. However, one of ordinary skill in the art will
readily recognize that the method can be used for multiple memory
cells, for example by utilizing a multiple bit line currents. A
word line current is turned on, via step 152. The word line current
generates the hard axis field used in programming a memory cell.
The appropriate bit line current is turned on, via step 154.
Preferably step 154 turns the bit line current on after the word
line current has been turned on. The bit line current generates the
easy axis field. Thus, the sign of the bit line current (positive
or negative) sets the direction of the easy axis field and,
therefore, the state of the magnetic memory cell. The bit line
current is turned off, via step 156. Step 156 preferably occurs
after a desired time interval has passed since the bit line current
was turned on. At a later time, the word line current is turned
off, via step 158.
[0040] FIG. 6B is a graph 160 depicting the word line current 162
and bit line current 164 versus time for programming of a magnetic
storage cell in a magnetic memory using the third embodiment of the
method in accordance with the present invention. The word line
current 162 is turned on to a value of Iw3 at time t1'". The bit
line current 164 is turned on at a time t2'" later to a value of
Ib4. At a time, t3'", later, the bit line current 164 is turned
off. After the bit line current 164 is off, the word line current
162 is turned off, at time t4'" later.
[0041] Because the word line current 162 is turned off after the
bit line current 164, the method 150 allows for more repeatable
programming of magnetic memory cells. The word line current and,
therefore, the hard axis field are turned off after the bit line
current and easy axis field. As a result, the magnetic moments at
the edges of the memory cell will be substantially the same for a
particular state of the magnetic memory cell. For example, the free
layer 60 depicted in FIG. 2A may be repeatably obtained. In other
words, the moments 62 and 64 will be in substantially the direction
shown in FIG. 2A. The remaining configurations depicted in FIGS. 2B
and 2C may generally be avoided. Thus, the field at which the
magnetic memory cell will switch is substantially the same.
Consequently, the hard and easy axis fields, and the corresponding
currents, required to program the memory cell will be substantially
the same. The state and, therefore, programming of the magnetic
memory cell can thus be repeatably obtained.
[0042] FIG. 7A is a graph 170 depicting a write-read test using one
embodiment of the method in accordance with the present invention
for programming a magnetic memory. FIG. 7B is a graph 180 depicting
a write-read test using a conventional method for programming a
magnetic memory. Referring to FIGS. 7A and 7B, the graph 170
indicates that all programming operations using a method in
accordance with the present invention are successful. However, as
can be seen in the graph 180, the low and high states are joined by
some lines, indicating that some programming operations failed when
conventional programming was used. Thus, using the methods 100,
110, 130, and/or 150 in accordance with the present invention,
performance of a magnetic memory can be improved.
[0043] FIG. 8 is a high-level block diagram of one embodiment of a
system 200 in accordance with the present invention for programming
a magnetic storage cell in a magnetic memory. The system 200
includes current source(s) 210 and an array of memory cells 220.
The methods 100, 110, 130, and/or 150 can be used to program cells
in the magnetic memory. The array 220 includes magnetic storage
cells that are preferably magnetic tunneling junctions, such as
those depicted in FIG. 1A and corresponding to the free layers of
FIGS. 2A-2C. The current source(s) 210 are used to provide the word
line and bit line currents in the method 110, 110, 130, and/or 150.
Thus, although a single connection to the array 220 is shown, the
current source(s) 210 are typically connected via word lines and
bit lines. In addition, in a preferred embodiment, the current
source(s) include at least one source for providing the word line
current and at least one separate source for providing the bit line
current.
[0044] In operation, the current source(s) 210 provide the word
line currents and bit line currents as described in the methods
100, 110, 130, or 150. Thus, the current source(s) 210 preferably
turn on a word line current to selected word lines, turn on an
appropriate bit line current for selected bit lines, and turn the
currents off as described in the methods 100, 110, 130, and/or 150.
Consequently, the system 200 can program memory cells of the array
220 more repeatably. Consequently, performance is improved.
[0045] A method and system has been disclosed for repeatably
programming a magnetic memory. Software written according to the
present invention is to be stored in some form of computer-readable
medium, such as memory, CD-ROM or transmitted over a network, and
executed by a processor. Consequently, a computer-readable medium
is intended to include a computer readable signal which, for
example, may be transmitted over a network. Although the present
invention has been described in accordance with the embodiments
shown, one of ordinary skill in the art will readily recognize that
there could be variations to the embodiments and those variations
would be within the spirit and scope of the present invention.
Accordingly, many modifications may be made by one of ordinary
skill in the art without departing from the spirit and scope of the
appended claims.
* * * * *